The objectives of the proposal are 1) to explore the usefulness of measurement of the frequency and amplitude of the closure sounds of porcine xenografts to determine if early and subclinical degeneration can be detected by this non-invasive method; 2) to explore whether the measurement of the frequency and amplitude of the aortic component of the second sound (A2) can assist in identifying early degenerative changes and subclinical stenosis of the natural aortic valve. We determined that the dominant frequency of A2 in patients with calcific aortic stenosis was higher than A2 in patients with normal aortic valves. In patients with porcine bioprosthetic valves in the aortic position, if the valves were implanted 1 1/2 years or less, A2 did not differ significantly from A2 produced by normal natural aortic valves. In patients with porcine xenografts in place 5-7 1/2 years, A2 was significantly higher and comparable to A2 in patients with calcific aortic stenosis. Continuation of this investigation relates to an exploration of the usefulness of the analysis of the frequency of the first heart sound in patients with porcine xenografts positioned in the mitral position to determine if an increased frequency may reflect subclinical degeneration. We also plan to evaluate A2 in adolescents and children with mild aortic stenosis to determine if mild disease of the aortic valve can be indentified by frequency analysis.